Conventional piston engines have a rotating crankshaft and stationary cylinder(s). This results in reciprocating pistons that must accelerate from and decelerate to stopped positions, causing vibration, bearing stress, and friction. The connecting rods of the pistons are not aligned with the axes of the cylinders except at the dead center points, resulting in lateral forces causing friction and wear of the piston seal rings and the cylinder inner surfaces. Relative movement between each connecting rod and piston necessitates a pivoting wrist pin connection between them, which ultimately results in an asymmetric velocity curve of the piston about the mid-point of piston travel making any engine with a piston wrist difficult to balance. Many attempts have been made to eliminate at least some of these disadvantages. For example, rotary piston engines have a stationary crankshaft surrounded by a radial array of cylinders that rotate around the crankshaft. This eliminates reciprocating parts, but causes high wind drag loss on the rotating cylinders, and produces strong gyroscopic effects of turning resistance and precession. The Wankel engine replaces pistons with a three-sided eccentric rotor. Gas turbines use rotationally symmetric rotors. Each engine type has unique advantages and disadvantages.